Aktiivilietemenetelmä

Aktiivilietemenetelmä, also known as the activated sludge process, is a widely used biological wastewater treatment method. It relies on the action of microorganisms, primarily bacteria, to remove organic matter and nutrients from sewage and other wastewater streams. The core of the process involves an aeration tank where wastewater is mixed with a microbial population called activated sludge. Air or oxygen is supplied to this tank, providing the necessary conditions for the aerobic bacteria to consume dissolved and suspended organic pollutants.

The activated sludge consists of a flocculent mass of bacteria, protozoa, and other microorganisms that form a complex ecosystem. As these microorganisms metabolize the pollutants, they multiply and grow, increasing the biomass of the activated sludge. After the aeration stage, the mixed liquor, a combination of treated wastewater and activated sludge, flows into a settling tank, also known as a clarifier. In the clarifier, the heavier activated sludge settles to the bottom by gravity.

A portion of this settled sludge, referred to as return activated sludge (RAS), is recirculated back to the aeration tank to maintain a sufficient concentration of microorganisms for effective treatment. The remaining sludge, known as waste activated sludge (WAS), is removed from the system for further treatment and disposal. The clarified water, now with significantly reduced levels of organic pollutants and nutrients, is discharged as effluent. The efficiency of the activated sludge process can be influenced by factors such as aeration rate, sludge age, temperature, and the characteristics of the influent wastewater.